Aircraft: PA28
Phase of flight: Cruise
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter VFR In IMC; Inflight Event / Encounter Weather / Turbulence

I filed IFR for my second flight of the day; from ZZZ1 to ZZZ2. The air had been smoky for my first flight; with 0.3 hours in actual IMC due to decreased visibility; and I suspected this flight would be the same. I requested ZZZZZ ZZZ3 ZZZ4 VXXX ZZZ5 direct. This would take me west of the fire and the associated TFR; which was centered on ZZZ VOR. I was given ZZZZZ ZZZ3 ZZZ ZZZZZ1; then as filed. This; of course; would take me right over the fire. I opened my IFR flight plan with ZZZ6 Approach and requested that I be rerouted around the fire. They told me I would have to ask Center. When I was switched to Center; the controller refused to reroute me; saying that the route they gave me was the 'preferred route' from my location to ZZZ2. I pointed out the fire directly below my route. The controller pointed out that the TFR ended at 9;000 ft. and I would be above that. I was already in smoke and my eyes were burning.As I was turned direct to ZZZ; I saw green radar reflections straight ahead of me on ADS-B in. I measured these; and they were 20nm away. There was a towering cumulus cloud directly in front of me that appeared to be closer than that. I requested the controller turn me right or left to avoid this convective activity. He refused; saying he would turn me southeast right before I got there. I was not satisfied with that; so I elected to divert to ZZZ6. He then gave me the arrival into ZZZ6 and handed me off to ZZZ6 Approach. As I descended toward ZZZ6; the engine monitor indicated the oil pressure was low. Because of that; I asked to make a precautionary landing at a closer airport. I was rerouted to ZZZ7 and I landed there without incident. I checked the oil upon landing; and it appeared adequate at five quarts. I did add oil.My flight the following day was uneventful. I did choose to fly to ZZZ8 first so I would not be given the same routing over the ZZZ Fire. This flight and the way Center handled it was concerning to me on multiple levels: As a single-engine piston pilot who did not have oxygen on board; I am breathing fumes from the fire. Also; the plane's engine requires oxygen for combustion. Flying through smoke is not ideal; especially when there is a safer route nearby. Not all convective activity involves rain; so it may not be visible on a controller's radar screen. We are taught the developing stage of a thunderstorm involves strong updrafts and no rain. As a single-engine piston pilot; I am not comfortable having a controller fly me right up to the precipitation he sees on his radar screen (which may be 20 minutes delayed) and then give me a turn. I suspect the display I saw using ADS-B in was the same one the controller saw on his screen. It was different from what I was seeing out the front window. Controllers need to listen to pilots. If I am reporting something different from what the controller is seeing on his radar display; he needs to take me seriously. The route I requested was not fundamentally different from the one ATC gave to me. It would have been safer and would have avoided the issues I encountered on this flight. Pilot reported being denied a request to reroute around a wildfire TFR and convective activity. Pilot diverted to avoid the adverse conditions.